The present invention relates to a rim rolling method in which a disk-like blank is used and a rim is formed by rolling on an outer peripheral portion of a web, a preforming roller die which is to be used in the rolling method, and a method of producing a brake shoe by using the rolling method.
As a method in which, during production of a sheet metal V-pulley, a disk-like blank is used and a rim is formed by performing a rolling process on an outer peripheral portion of a web, for example, a rolling method is disclosed in Japanese Patent No. 2520095. In the rim rolling method, the outer peripheral portion of a disk-like metal blank is slit in the thickness direction into two parts by a slitting roller die, thereby expandingly forming a rim. In the slitting roller die used in the method, an edge-like blade portion protrudes in the circumferential direction in an axial center portion of the outer peripheral face. While pressing the edge-like blade portion against a center portion in the thickness direction of the outer peripheral face of the blank, the slitting roller die and the blank are synchronously rotated, whereby the outer peripheral portion of the blank is slit in the thickness direction into two parts so that a rim is annularly expandingly formed.
In the above-mentioned rim rolling method in which the slitting roller die is pressed against the outer peripheral face of the blank from the beginning, the edge of the blade portion of the slitting roller die easily slips over the outer peripheral face of the blank in the thickness direction during an initial stage of the slitting process, and hence it is not easy to slit the outer peripheral face of the blank at an arbitrary position in the thickness direction. In the case where a thin blank is used, particularly, instability and difficulty of centering and equal slitting in the process of slitting a center portion in the thickness direction of the outer peripheral face of the blank are conspicuous.
Therefore, it is an object of the invention to provide a rim rolling method in which slitting can be correctly performed at an arbitrary position in the thickness direction of an outer peripheral face of a blank. It is also an object of the invention to provide a preforming roller die which is to be used in the rim rolling method. It is a still further object of the invention to provide a method of producing a brake shoe by using the rim rolling method.
The rim rolling method includes: a preforming step of forming an outer peripheral groove in the entire outer peripheral portion of a disk-like metal blank; and an expandingly forming step of expanding the outer peripheral groove of the blank in a thickness direction to form a rim. In the preforming step, a preforming roller die is used in which a groove having a width that is larger than the thickness of the blank is formed in an outer peripheral face in a circumferential direction and a groove forming blade portion protrudes in the circumferential direction on an inner bottom portion of the groove, and the groove and the groove forming blade portion of the preforming roller die are pressed against an outer peripheral portion of the blank to form the outer peripheral groove in the entire outer peripheral portion of the blank by the groove forming blade portion. In the expandingly forming step, an expandingly forming roller die is used in which an expanding blade portion protrudes from an outer peripheral face in a circumferential direction, and the expanding blade portion of the expandingly forming roller die is pressed against the outer peripheral groove of the blank, whereby the outer peripheral portion of the blank is slit in the thickness direction into two parts to expandingly form a rim.
According to the rim rolling method, in advance of the process of slitting the outer peripheral portion of the blank in the thickness direction into two parts by the expandingly forming roller die to expandingly form a rim the preforming roller die is used which has the groove and the groove forming blade portion in the outer peripheral face, and the groove and the groove forming blade portion of the preforming roller die are pressed against the outer peripheral portion of the blank, so that the outer peripheral groove is formed in the entire outer peripheral portion of the blank by the groove forming blade portion. During the expandingly forming process, therefore, the expanding blade portion of the expandingly forming roller die can be pressed against the outer peripheral groove without slipping over the outer peripheral face of the blank. When the groove forming blade portion is disposed in the groove of the preforming roller die so as to correspond to a desired slitting position of the outer peripheral face of the blank, consequently, slitting can be correctly performed at an arbitrary position in the thickness direction of the outer peripheral face of the blank.
In the preforming step, at the same time when the outer peripheral groove is formed in the entire outer peripheral portion of the blank by pressing the groove and the groove forming blade portion of the preforming roller die, the outer peripheral portion of the blank may be thickened in the groove. According to this configuration, a rim having desired thickness and width dimensions can be obtained even in the case where a thin blank is used.
In the preforming roller die of a further aspect of the invention, a groove having a width that is larger than a thickness of a blank is formed in an outer peripheral face in a circumferential direction, and a groove forming blade portion protrudes in the circumferential direction on an inner bottom portion of the groove. When the preforming roller die is used, a preforming process in which the groove and the groove forming blade portion are pressed against an outer peripheral portion of the blank to form an outer peripheral groove in the whole outer peripheral portion of the blank can be performed easily and surely. Preferably, the groove may be formed into a V-like section shape which is gradually expanded as moving toward an outside.
The further aspect of the invention is a method of producing a brake shoe by using a disk-like metal blank, the brake shoe having a shoe rim which has a partially arcuate shape, and a shoe rib which protrudes from an inner periphery of the shoe rim, the method including: a preforming step of forming an outer peripheral groove in a whole outer peripheral portion of the blank; an expandingly forming step of expanding the outer peripheral groove of the blank in a thickness direction to form a web and a rim; a step of forming the brake shoe from the web and the rim. In the preforming step, a preforming roller die in which a groove having a width that is larger than the thickness of the blank is formed in an outer peripheral face in a circumferential direction and a groove forming blade portion which protrudes in the circumferential direction on an inner bottom portion of the groove is used, and the groove and the groove forming blade portion of the roller die are pressed against an outer peripheral portion of the blank to form the outer peripheral groove in the entire outer peripheral portion of the blank by the groove forming blade portion. In the expandingly forming step, an expandingly forming roller die is used in which an expanding blade portion protrudes from an outer peripheral face in a circumferential direction, and the expanding blade portion of the roller die is pressed against the outer peripheral groove of the blank, whereby the web and the rim on an outer peripheral portion of the web are formed while slitting the outer peripheral portion of the blank in the thickness direction into two parts. In the brake shoe forming step, the web and the rim are cut into a required shape, thereby forming a brake shoe having a shoe rim which has a partially arcuate shape, and a shoe rib which protrudes from an inner periphery of the shoe rim.
According to the method of producing a brake shoe, a brake shoe having a shoe rim which has a partially arcuate shape, and a shoe rib which protrudes from an inner periphery of the shoe rim can be easily produced from a disk-like metal blank.